Reptilia NEET Special

Reptilia

Reptila were originated during carboniferous period of palaeozoic era. Mesozoic era is Golden age of Reptile.

The branch of biology which deals with the study of reptiles is known as "Herpatology".

Class Reptila’s animals are the first successful terrestrial animals.

First reptiles are called stem reptilia or Cotylosours.



General Characters of Reptilia

These are, normally, terrestrial animals, but some animals are aquatic in nature also.

Body is divided into head, neck, trunk and tail.

Their skin is dry, cornified, rough, nong-landular (Femora; gland in male lizard).

In these animals, each limb has five digits. Each digit has mcurved nails.

Some lizards and snakes do not have limbs e.g.Ophiosaurus lizard is a limbless lizard is a limbless exoskeleton is made up of horny epidermal scales or bony scales or bony plates. A complete alimentary canal is found in these animals, which opens into cloaca.

Teeth are acrodont and thecodont pleurodent type.

Tongue is protrusible.

Respiration in these animals is by lungs, through out the life, but members of order Chelonia can respire through their cloaca, it is known as "Cloacal respiration".

In these animals, heart is incompletely four chambered with 2 complete auricles and two incomplete ventricles. Right and left both systemic arches are present.

Ventricle of animals of order crocodifia is completely divided into two, i.e. heart is four chambered in crocodiles.

Sinus venosus is ill developed and truncus arterious is absent. RBCs are oval and nucleated.

Endoskeleton of these animals is made up of bones.

Only one occipital condyle is present in skull, this type of skull is called monocondyl skull. Ribs are present in neck and thorax ribs of thoracic region make true sternum.

Centrum of vertebrae are procoelus type. Sternum is well developed. Sternal ribs are found in reptiles.

A chevron bone is found in caudal vertebrae of these animals.

One pair of metanephric kidneys help in excretion. These animals are uricotelic for water conservation.

There are 12 - pairs of cranial nerves in these animals.Brain is well developed.       

Lateral line system is absent. At the roof/ceiling of buccal cavity Jacobson's organ (olfactory) is present.

Genital aperture is not separate from anus. Ureters, genital ducts and alimentary canal open into a single cloacal aperture.

These are unisexual animals. Fertilization is internal.

One or two penis (Hemipenis) is found in male animals as copulatory organ.

These are mostly oviparous, but some animals are viviparous also. Amount of yolk is very much in their eggs, i.e. eggs are Polylecithal & Telolecithal.

Eggs are cleidoic, i.e. eggs are covered by a shell made up of CaCO3·

Cleidoic eggs is an adaptation for terrestrial habitat. Eggs are leathery.

All the three embryonic membranes amnion, chorion and allantois are present in the embryo. Yolksac is also attached with embryo. So this class is grouped under Amniota group.

Cleavage is discoidal, meroblastic.

Development direct i.e. larva stage is absent.

Parental care is often marked.

hese are cold blooded, poikilothermal animals.

Their body temperature varies according to climate.

Class Reptilia is classified on the basis of presence or absence of temporal fossae in the temporal region of skull and on their number.

Class reptilia is divided into following major five sub-classes

(1)    Anapsida

(5)    Diapsida

Subclass - Anapsida

Temporal fossae are absent in the temporal region of the skull i.e. roof of skull is complete.

Limbs are strong.

(1)    Order - Cotylosauria

e.g. Seymauria: Connecting link between Amphibia and Reptilia.

(2)    Order - Chelonia

Body is broad and oval.

They are terrestrial, marine and freshwater animals.

This order includes live and extinct both the animals.

Whole body is covered by firm bony shell.Exoskeleton of dorsal region of body is called carapace and skeleton of ventral region of body is called plastron.

Jaws are horny and teeth less, beak like jaws are found.  

Sternum is absent:

Bony plate present on the body are called osteoderms.

Nails are found on digits. Web or membrane is found in the digits for swimming.

Scales are found on neck, limbs and tail.

All these three organs can be pushed into the carapace.

Thoracic vertebrate and ribs are attached with carapace.

Cloacal aperture is vertical and it helps in respiration.

Single copulatory organ is found in male animal.

Animals are oviparous.

e.g.  

Testudo - Land tortoise

Trionyx - Fresh water terrapins (edible)

Chelone – Marine’ (tortoises) turtles

Kachhugra tactum



Sub-class - Diapsida

One pair superior and one pair inferior temporal fossae are found in the temporal region of skull.

Subclass Diapsida is divided into two super orders

(1)    Lepidosauria

(2)    Archosauria

(1)    Super order Lepidosauria:

This super oreer-is divided into two orders.

(1)    Order - Rynchocephalia

Most of the species of this order are found in the form of fossils.

Only Sphenodon punctatum species is live only. It is found in New Zealand.

Body is small and lizard like. Tail is compressed laterally.

Limbs are pentadactyl and digits are with nails.

A functional third eye or pineal or parietal eye is found in the head.

Vertebrae are amphicoelus type.

Teeth are acrodont type.

Penis or copulatory organ is absent in male animals.

Long living » 100 years

 e.g; Sphenodon punctatum - Tuatara (living fossil) It is found only in Newzealand.

(2)    Order - Squamata:

Largest number of species of reptiles is found in this order in modern era. All the lizards & snakes are included in this order.

One or two pairs of temporal fossal are found in temporal region of skull, which disappear after sometimes.

Limbs clawed, Limbs are absent in snakes and some of the lizards.

Horny scales are found on body, i.e. their exoskeleton is made up of horny plates.

Vertebrae are procoelus type.

Teeth are pleurodont, i.e. tooth is situated at lateral side of jaw bone.

Copulatory organs are can be seen paired (hemipenis).

Autotomy phenomenon in lizards.

Order squamata is divided into two suborders Suborder

(i)     Lacertilia Suborder

(ii)    Ophidia

Suborder (i) Lacertilia:

Normally the members of this suborder is "Lizards"

Study of lizards is called "Saurology",

Limbs and girdles are well developed in these animals.

Eyelids are movable and nictitating membrane is found in eye.

Auditory aperture or auditory opening and tympanum is present

Urinary bladder is present

Foramen of panizzae is present in the heart of lizard.

e.g.

Hemidactylus - Common lizard, wall lizard. It can shed its own tail at the time of emergency.



It is called autotomy. Power of regeneration is well marked.

Calotes - Blood sucker, Garden lizard (Girgit). It can change its colour according to environment.

Draco - Flying lizard. Its body skin expands in the form of 2 wings or patagia. With the help of these patagia, it can glide from one tree to another tree or its branches. It can not fly.

Chameleon - Arboreal lizard (Viviparous) (Girgit)

Varanus - Goh, Monitor lizard.

Varanus komodoensis -Ferocious Dragon - Largest living lizard

Ophio-saurus - It is limbless lizard. It is also called glass - snake.

Anguis - limbless lizard

Burkudia - limbless lizard found in south India.

Heloderma - Gila - monstor, Hela monster. It is the only poisonous lizard. Its poison glands are modified sublingual glands (Mexico & USA).

Mabuya - Viviparous lizard.

Phrynosoma - Horned toad (viviparous)

Amblyrhynchus - Marine lizard

Uromastix - Sand lizard or Sand a

Suborder (ii) Ophidia:

Members of this suborder are normally called "Snakes".

The study of snakes is called ophiology or serpantology.

Body long, thin, smooth and limbless,

Eyelids are immovable and nictitating membrane - in eyes are absent.

Girdles, sternum and urinary bladder absent.

Auditory opening and tympanum absent. No middle ear

Tongue thin, long and bifid and sensitive to odour­ and vibration.

Left lung is ill developed.

Leathery shell is found on egg of Snakes. e.g.

Python molurus - Azgar. It is the largest snake, its length is about 5 feet. Rudiments of hind limbs are found on the body. It is non-poisonous snake.

Ptyas mucosus - Zamenis or Rat snake. It is commonly called Dhaman. It feeds on rats, so it is also called "Friend of farmer". It is non-poisonous snake.

Eryx Johni - Sand boa. It is also called Dumuhi snak. It is a non-poisonous snake.

Typhlops - Blind snake. Non-poisonous

Hydrophis - Marine snake. It is a deadly poisonous snake. Its tail is laterally compressed. It is a viviparous snake.

Enhydrira - Sea snake

Naja - Indian cobra, poisonous snake. Its poison is neurotoxic.

Naja bungarus or N.Hannah - King cobra, poisonous snake. It is the largest snake and poisonous snakes (Head with one or two circular mark).

Bungarus - Krait: Poisonous (neurotoxic) snake Vipera - Viper snake: Head is differentiated from body. Poisonous snake (viviparous). Its venum is haemotoxic/Cardiotoxic. Loreal pit is found which is a thermoreceptor. Largest viper is Russel viper (N mark on head).

Micrurus - Coral snake.

Crotalus - Rattle snake: It produces a characteristic rattling sound of "Rate-raterate", so it is called rattle snake. It is poisonous and ovo-viviparous snake.

Characteristic features of poisonous snakes:

Small scales are found on head or hood.

Laterally compressed tail is present in marine snake.

Ventrally placed scales of the body arc broad.

Two teeth mark is of poisonous snake. (V-shaped - Non poisonous)

Poison glands of poisonous snakes are modified labial glands. These are homologous to salivary glands of Mammals.

Poisonous teeth (fangs) are modified maxillary teeth.

Treatment of poisonous snake bite is done by Anti­venom dose.

Anti-venom is produced at

(1)    Central Research Institute Kausuali - Shimla

(2)    Hoffkine Institute, Mumbai.

Biggest Serpentorium is located in India-Chennai

(2)    Super order - Archosaurea

This super order is classified into

(1)    Order - Crocodilia or Loricata

(2)    Order - Saurischia

Order - Crocodilia or Loricata

Crocodiles, alligator etc. are included in this order.

These are amphibious in nature these live in lakes or rivers.

These are largest modern reptiles.

Skin is covered by lines of bony scutes

Body is solid and massive.

Snout is long. External nares are situated at the distal end of snout and nares have cover also.

Diaphragm is present in between thorax and abdomen.

Sternum and abdominal ribs are present.



Special features:

- Heart is completely four chambered

- Ventricle is completely divided into two chambers.

- Teeth are thecodont type.

Urinary bladder absent

A median erectile grooved penis is present in male animals e.g.

Crocodylus/Crocodilus (Crocodile) - It is only found in

Indian subcontinent.

Gavialius - Gharial. Snout very long.

Alligator - Mexican crocodile.

Order - Saurischia

Order of reptilian pinosaurs (fossils)

Found in Jurassic, Triassic period of Mesozoic era Extinct in Creataceous period of Mesozoic era.

e.g.

Brontosaurus - Thunder lizard. Largest Dinosaurs (Herbivorous).

Stegosaurus

Tyrannosaurus - Tyrant lizard. King of Dinosaurs 

Review

Reptilia (reptiles): Dry scaly waterproof skin, digits of all the four limbs armed with claws, well developed lungs for air breathing, incompletely 4- chambered heart in most cases, males with copulatory organs, eggs amniotic and laid on land, fertilization internal, no larval stage.